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  • 6/27/2007

Babies Shed Light on 'Friendly' Bacteria


Examining a baby's stool may not be every new parent's favorite pastime, but a look at those early "samples" is helping scientists discover how microbes grow in the infant gut.

In the study, researchers from the Stanford University School of Medicine collected more than 500 stool samples from babies during their first year of life.

Before birth, a baby's gut is sterile and completely free from microbes. Within days, helpful microbes establish a thriving community that soon outnumbers the baby's own cells 10-fold -- a ratio that persists throughout life.

These microbes play critical roles in health, including processing nutrients, defining host body-fat content and providing protection against invading pathogens.

While researchers know some of the complex roles of the community of microbes found in humans' guts, how this ecosystem develops and flourishes remains a mystery.

"It's an amazing thing trying to figure out how we go from a completely sterile gut to having a microbial ecosystem that will be with us for the rest of our lives," study senior author Dr. Patrick Brown, a professor of biochemistry, said in a prepared statement. "What can be more fundamental than that?"

Brown and his colleagues looked at stool samples from 14 healthy, full-term infants over their first year of life.

They found that each baby had very different microbes colonizing their intestinal tracts, and at different stages.

"This study emphasizes that the definition of a 'healthy' baby is pretty broad," lead author Chana Palmer, a graduate student in Brown's lab at the time work was done, said in a prepared statement.

By the end of their first year, each baby had a unique intestinal ecology that harbored societies of microbes similar to that found in adults' intestines.

In the six babies who received antimicrobial medicine during the first year, only one had an extremely dramatic change in the microbial community in response to the drugs.

"But it was so dramatic, it makes us want to look at more examples of that and try to understand generalizations of the process," Palmer said.

Interestingly, two of the babies were fraternal twins delivered by Caesarean section and thus without any exposure to the mother's vaginal or rectal environments. The twins had much lower bacterial levels than the other babies for the first week of life, and they also showed the most similarity in their microbial profiles.

"The fact that the twins were so similar gives us a glimmer of hope that it's not a completely chaotic process," said Palmer.

This study helps uncover the range of what occurs in the guts of healthy babies born to healthy mothers. Future studies could explore the roles genetics and environment play in the development of these microbes, such as how the microbial environments of breast-fed babies compare to formula-fed babies.


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